Treatment of pyrites

ABSTRACT

PROCESS FOR TREATING PYRITES WHEREIN THE PYRITES IS DIRECTLY CONTACTED WITH AN INERT GAS UNDER CONDITIONS TO PRODUCE PYRROHTITE BY FREEING THE LABILE SULFUR FROM THE PYRITES, THE INERT GAS PROVIDING THE HEAT REQUIREMENTS FOR THE SULFUR DISTILLATION. THE SULFUR IS RECOVERED FROM THE INERT GAS AND THE INERT GAS INDIRECTLY HEATED BY AN OFF-GAS PRODUCED IN ROASTING THE PYRROHTITE FOR SUBSEQUENT PASSING TO THE SULFUR DISTILLATION.

June 20, 1972 N. E. MAsclo 3,671,197

TREATMENT OF PYRITES Filed Feb. 5, 1970 ATTORNEYS United States Patent O3,671,197 TREATMENT OF PYRITES Nicholas E. Mascio, Verona, and Robert F.Burke, Riverdale, NJ., assignors to The Lummus Company, Bloomfield, NJ.

Filed Feb. 5, 1970, Ser. No. 8,837 Int. Cl. C21b 1 04 U.S. Cl. 23-200 13Claims ABSTRACT F THE DISCLOSURE Process for treating pyrites whereinthe pyrites is directly contacted with an inert gas under conditions toproduce pyrrohtite by freeing the labile sulfur from the pyrites, theinert gas providing the heat requirements for the sulfur distillation.The sulfur is recovered from the inert gas and the inert gas indirectlyheated by an off-gas produced in roasting the pyrrohtite for subsequentpassing to the sulfur distillation;

This invention relates to the treatment of pyrites and more particularlyto a new and improved process for producing sulfur and iron oxxide fromiron pyrites.

The Imineral pyrite is generally characterized as FeS2, though thestoichiometry is not exact. Numerous processing schemes have beendeveloped in an attempt to economically produce iron oxide and sulfurfrom pyrites, but such schemes have met with little success. In general,these processes involve a first step for freeing labile sulfur from thepyrites as represented by the following equation:

and the resulting pyrrohtite is then roasted with an oxygen containinggas to produce the iron oxide, as represented by the following equation:

The processing step for freeing labile sulfur is endothermic andtherefore the high fuel requirements for this step have made the overallprocess unattractive.

In an attempt to reduce the fuel requirements for the initial processingstep numerous schemes were developed wherein the hot sulfurdioxide-containing gas generated in the roasting step is employed todirectly heat the pyrites for removal of labile sulfur. These processingschemes have also met with little success as a result of poor yields ofsulfur and/or iron oxide and/or the presence of unacceptable amounts ofsulfur in the iron oxide product.

Accordingly, an object of this invention is to provide a new andimproved process for producing iron oxide and sulfur from pyrites.

Another object of this invention is to provide a process for treatingpyrites which produces sulfur and iron oxide of acceptable quality inacceptable yields.

A further object of this invention is to provide a process for treatingpyrites which lowers overall fuel requirements.

These and other objects of the invention should be more readily apparentfrom reading the following detailed description of the invention withreference to the accompanying drawing wherein:

The drawing is a simplified schematic ow diagram of an embodiment ofthis invention.

The objects of this invention are broadly accomplished by heating aninert gas by indirect heat transfer with the hot off-gas from thepyrrohtite roaster and directly contacting pyrites with the heated inertgas to remove the labile sulfur therefrom, thereby meeting at least aportion of the heat requirements, and preferably essentially all of theheat requirements, of the endothermic sulfur distillation step with theheat generated in the exothermic pyrrohtite roasting. In this manner,fuel requirements are reduced and the sulfur distillation steps andpyrrohtite roasting may be separately regulated to produce sulfur andiron oxide, respectively, of acceptable quality and in acceptableyields.

The removal of labile sulfur from pyrites is effected by directlycontacting the pyrites with the inert gas which is provided at atemperature and in a quantity suicient to meet the heat requirements ofthis reaction. In addition, the temperature of the inert gas must be ata value to insure that the vapor pressure of sulfur in the gas stream,if any, is slightly less than that in equilibrium with the pyrites atthe operating temperature and pressure. In general, the labile sulfur isremoved from the pyrites at temperatures from about 600 C. to about 1000C., preferably from about -600 C. to about 650 C. and pressures fromabout -10l H2O to about +10" H2O, with respect to atmospheric pressure,and preferably at a pressure of about 0" H2O (atmospheric pressure). Theinert gas employed may be any gas which does not adversely aifect thesulfur distillation; i.e., inert with respect to the oxidation ofsulfur, and as representative examples of such gases, there may bementioned: nitrogen, sulfur dioxide and the like.

The pyrrohtite roasting is generally effected with an excess of oxygen;i.e., an excess of the stoichiometric roasting requirements, at bedtemperatures from about 11000 C. to about 1050 C., preferably from about1020 C. to about 1035 C., and at pressures from about 5" H2O to about 0"H20, with respect to atmospheric pressure. The use of temperatureswithin the hereinabove noted narrow temperature range and an excess ofoxygen, results in an acceptable production rate of an iron oxide cinderlow in sulfur.

The invention isfurther described with respect to an embodiment thereofillustrated in the accompanying drawing, but it is to be understood thatthe scope of the invention is not limited by this embodiment. It isfurther to be understood that various equipments, such as pumps, valves,heat exchangers, etc. have been omitted from the drawing to facilitatedescription thereof, and the placing of such equipment at appropriateplaces is within th scope of those skilled in the art.

Referring now YAto the drawing, a drying gas, such as air, in line 10 ispassed through heat exchanger 11 wherein the air is heated by indirectheat transfer with a roaster off-gas, as hereinafter described. Theheated air from heat exchanger 11 in line 12 is introduced into oneiendof a suitable drier 13, such as a rotary lkiln or fluidized unit, with akiln being preferred, along with moisture containing pyrite in line 14.The pyrite introduced into the drier 13 generally has a moisture contentin the vicinity of about 10% and as a result of the direct cocurrentcontact between the pyrite and heated air, the moisture content of thepyrite is reduced to about 0.1

be an ore or a concentrate, suchas tailings from a copper concentrator.If in the form of an ore, the size of the feed is generally from about1-2 mm. and if in the form of a concentrate the size of the feed isgenerally from about 22S-325 mesh.

Moisture laden drying air is withdrawn from drier 13 through line 14,introduced into a cyclone separator 15 to separate pyrite dust therefromand the moisture laden air is released to the atmosphere through line16.

The dried pyrite is withdrawn from drier 13 through line 17, combinedwith dust removed from cyclone separator 15 through line 18, andintroduced into a pyrite sublirnator 21 such as a rotary kiln orfluidized unit, with a kiln being preferred, to separate labile sulfurtherefrom. A heated inert gas, such as nitrogen, which may also containuncondensed sulfur, is introduced into sublimator 21 through line 22 andcountercurrently contacts the pyrites therein. The inert gas isintroduced at a temperature and in a quantity to both provide the heatrequirements for freeing labile sulfur from the pyrite and maintain areaction bed temperature within the hereinabove described range. Inaddition, if the inert gas contains uncondensed sulfur, the temperatureat which the inert gas is introduced should be at a value at which thevapor pressure of such sulfur is less than the vapor pressure of thesulfur in equilibrium with the pyrites in the sublimator 21 at theprevailing temperatures and pressure. It should be readily apparent thatthe quantities and temperatures of both the inert gas and pyrites may bevaried to provide the desired operating conditions for the sublimator.As a result of the countercurrent contact between the pyrites and thehot inert gas, the labile sulfur is freed from the pyrites(approximately 85-98%) producing pyrrohtite.

The inert gas, now containing sulfur vapor, is withdrawn from thesublimator 22 at a temperature above the dew point of the sulfurcontained therein and introduced into a cyclone separator 24 to separateany pyrrohtite dust contained therein. The sulfur containing inert gasis withdrawn from cyclone separator 24 through line 25 and passed tosulfur recovery, as hereinafter described.

Solids, containing mainly pyrrohtite and some unreacted pyrite, iswithdrawn from sublimator 21 through line 26, combined with any dustrecovered from cyclone separator 24 through line 27, and introduced intoa roaster 28, preferably a fluid bed roaster, along with a molecularoxygen-containing gas, such as air in line 31. The roaster 28 isoperated at the temperature and pressure conditions hereinabove notedand preferably with an excess of oxygen, to produce sulfur dioxide andiron oxide, as hematite (Fe203).

The iron oxide cinder is withdrawn from roaster 28 through line 32 and ahot sulfur dioxide-containing gas is withdrawn therefrom through line33. The sulfur dioxide-containing gas in line 33 is introduced intocyclone separator 34 to separate any iron oxide contained therein whichis withdrawn through line 35 and combined with the iron oxide in line32. The sulfur dioxide containing gas from cyclone separator 34 in line36 is passed through heat exchanger 37 to indirectly heat the inert gasbeing passed to sublimator 21 as hereinafter described. The cooledsulfur-dioxide containing gas from heat exchanger 37 in line 38 ispassed through heat exchanger 11 to indirectly heat the drying air inline and then passed to further recovery through line 39, e.g., reactionwith hydrogen sulfide, if available, to produce sulfur; production ofsulfuric acid, or the like.

The inert gas, containing elemental sulfur, from cyclohe separator 24 inline 25 is passed through heat exchanger 41 to effect cooling thereof byindirect heat transfer with an inert gas from a sulfur recovery zone, ashereinafter described, and the cooled gas in line 42 is introduced intoa sulfur recovery zone, schematically designated as 43. 'I'he sulfurrecovery zone 43 may include any one of a wide variety of processingtechniques for separating sulfur from a gas, including, for example,sulfur scrubbing, or sulfur absorbing, and the like. These processingtechniques are generally known in the art and therefore no detaileddescription thereof is deemed necessary for an understanding of theinvention.

An inert gas, containing minor amounts of sulfur, is Withdrawn fromsulfur recovery zone 43 through line 44 and passed through heatexchanger 41 to effect heating thereof by indirect heat transfer withthe sulfur-containing inert gas in line 25. The heated inert gas fromheat exchanger 41 in line 45 is passed through heat exchanger 37 toeffect heating thereof by indirect heat transfer with the sulfurdioxide-containing gas in line 36 and the heated inert gas is passedthrough line 22 to sublimator 21, aS hereinabove described.

Numerous modications of the hereinabove described embodiment arepossible within the spirit and scope of the invention. Thus, forexample, in some operations total heat recovery may not be economicaland, therefore, a portion of the heating requirements for maintainingthe inert gas at the proper operating temperature may be provided bysupplemental heating, i.e., the sulfur dioxide offgas does not provideall of the heating requirements for maintaining the inert gas at theproper operating temperature.

The process of the invention is extremely effective for providing ironoxide and sulfur from pyrites. The use of an inert gas to transfer heatevolved from the exothermic roasting of pyrrohtite to the endothermiciron pyrites distillation to free the labile sulfur reduces overall fuelrequirements. In addition, this transfer of heat is effected in a mannersuch that the processing conditions for freeing labile sulfur, roastingpyrrohtite and providing heat to the inert gas are each independentlyVariable and therefore may be separately regulated. Thus, the roastingoperation,V unlike prior art processes, may be operated at conditionsparticularly suited for producing iron oxide in acceptable quality andat acceptable yields, i.e., an excess of oxygen and temperature controlwithin a narrow range. Similarly, the temperature, heat content andquantity of the inert gas may be controlled in a manner to provide theoptimum conditions for the freeing of the labile sulfur of the pyrites.

In addition, the processing scheme should include provisions forsupplying make-up inert gas at an appropriate place to offset inert gasleakage.

Furthermore, the inert gas and pyrites may be contacted cocurrentlyinstead of countercurrently as particularly described, althoughcountercurrent contact is preferred. As still another modification, thedrying of iron pyrites may be effected in a manner other than asparticularly described or with a drying gas other than air, provided thegas is inert with respect to the pyrites. The above modifications andnumerous other modifications should be apparent to those skilled in theart from the description herein.

The following example is illustrative of conditions for the process ofthe invention and it is to be understood that the scope of the inventionis not to be limited thereby.

EXAMPLE The processing conditions tabulated below may be employed forproducing 540 short tons per day (st./d.) of Fe203 and 191 short tonsper day of sulfur. The pyrites is supplied through line 14 at the rateof 1000 short tons per day (10 Wt. percent moisture) and is dried With30,000 s.c.f.m. of air in line 12 to a moisture content of 0.1 wt.percent.

The composition and rate of flow in each of the major streams are Iasbelow.

l P.s.i.g.

Numerous modifications and variations of the invention are possible inlight of the above teachings and therefore the invention may bepracticed otherwise than as particularly described.

What is claimed is: 1. In a process for producing 1ron oxlde from ironpyrites by freeing labile sulfur from the iron pyrites to therebyproduce pyrrohtite and roasting the pyrrohtite to produce iron oxide,the improvement comprising:

(a) directly contacting the pyrites with a hot inert gas which is inertwith respect to the oxidation of sulfur to provide heat requirement forremoving labile sulfur from the pyrites, thereby producing pyrrohtite;

(b) introducing the pyrrohtite into a roasting zone wherein thepyrrohtite is contacted with a molecular oxygen-containing gas at atemperature from about 1000 to about 1050 C. to produce a gaseous streamcontaining sulfur dioxide and iron oxide;

(c) separating sulfur from the inert gas recovered from step (a);

(d) passing the inert gas in an indirect heat transfer relationship withthe sulfur dioxide containing gas from step (b) to effect heating of theinert gas; and

(e) passing heated inert gas to step (a).

2. The process as defined in claim 1 wherein the contacting of step (a)is effected at a temperature from about 600 C. to about 1000 C.

3. The process as defined in claim 2 wherein the roasting is effectedwith an excess of oxygen.

4. The process as defined in claim 3 wherein the roasting zone ismaintained at a temperature from about 1020 C. to about 1035 C.

5. The process as defined in claim 1 wherein the contacting of step (a)is effected at a temperature from about 600 C. to about 650 C.

6. The process as defined in claim 1 wherein the inert gas is nitrogen7. The process as defined in claim 1 wherein the molecularoxygen-containing gas is air.

8. A process for producing sulfur and iron oxide from iron pyrites,comprising:

(a) introducing pyrites into a first zone wherein the pyrites isdirectly contacted with an inert gas which is inert with respect to theoxidation of sulfur, said inert gas being introduced at and in aquantity to maintain a temperature from about 600 C. to about 1000 C.and to provide a vapor pressure of sulfur in the inert gas which is lessthan that which is in equilibrium with the pyrites at the conditions inthe first zone, said inert gas providing heat requirements to freelabile sulfur and produce pyrrohtite;

(b) introducing the pyrrohtite into a second reaction zone with amolecular oxygen-containing gas, said gas being introduced in an amountto provide oxygen in excess of stoichiometric requirements, said secondreaction zone being maintained at a temperature from about 1000 C. toabout 1050 C. to produce a gaseous stream containing sulfur dioxide andiron oxide;

(c) withdrawing inert gas, containing gaseous sulfur, from the reactionzone and introducing the inert gas into a sulfur recovery zone whereinsulfur is recovered therefrom;

(d) passing inert gas from the sulfur recovery zone in an indirect heattransfer relationship with the gaseous stream, containing sulfurdioxide, withdrawn from the second reaction zone to effect heating ofthe inert gas; and

(e) passing the heated inert gas to the first reaction zone.

9. The process as defined in claim 8 wherein the process is a continuousprocess and the pyrites and inert gas are countercurrently contacted inthe first reaction zone.

10. The process as defined in claim 8 wherein the first reaction zone ismaintained at a temperature from about 600 C. to about 650 C. and thesecond reaction zone is maintained at a temperature from about 1020 C.to about 1035 C.

11. The process as defined to claim 8 wherein the inert gas is nitrogen.

12. The process as defined in claim 8 wherein the pyrites is dried priorto introduction thereof into the first reaction zone by direct contactwith a hot drying gas, said hot drying gas being heated by indirect heattransfer with the gaseous stream, containing sulfur dioxide, after theheat transfer step with the inert gas.

13. The process is defined in claim 8 wherein the pressure in said firstzone is maintained at from about 10" 7 H2O vto about +10 H2O withrespect to atmospheric pressure.

References Cited UNITED STATES PATENTS Jukkola 23-1177 X Heath 23-224Fogh 23-227 Aanerud 23--227 Bacon et al 75--9 Clark 23-227 X 8 1,971,8158/ 1934 Halvorsen 23-200 2,785,050 3/ 1957 Swaine et al 23-200 X FOREIGNPATENTS 5 731,527 Y 6/ 1955 Great Britain 75-9 OSCAR R. VERTIZ, PrimaryExaminer G. O. PETERS, Assistant Examiner 10 U.s. c1. X.R.

